therapeutic window

1:  the range of dosage of a drug or of its concentration in a bodily system that provides safe effective therapy the narrow therapeutic window…the effect may go from therapeutic to toxic with an increase of just 10 micrograms per milliliter [in] blood concentration—Lisa Davis

2:  a usually short time interval (as after a precipitating event) during which a particular therapy can be given safely and effectively has a narrow therapeutic window: the drug must be given within three hours of a stroke in order to be effective—Genesis Report-RX